The present invention relates generally to the field of receivers which use acousto-optic delay lines to analyze signals such as radar pulses present in the electronic warfare (EW) environment: and more particularly to EW receivers which includes angle-of-arrival and instantaneous frequency measurement capability.
An interferometric Bragg cell used with a laser has been previously investigated and demonstrated as a spectral analysis device by the Avionics Laboratory of the U.S. Air Force for EW applications. The interferometric Bragg cell consists of a reference Bragg cell and a signal Bragg cell. The reference Bragg cell is modulated with a chirp signal. A selected band of the EW signal environment modulates the signal Bragg cell. The output of the reference Bragg cell and signal Bragg cell are combined and result in a channelized spectral output with each channel at the same intermediate frequency (IF).
A conventional phase comparison angle-of-arrival (AOA) system to cover a wide frequency range (FIG. 1) mixes signals from quadrant antennas via delay lines with a local oscillator signal which is controlled by a frequency measurement receiver having an omni-directional antenna.
Berg et al U.S. Pat. No. 4,326,778 discloses an acousto-optic time integrating correlator which uses a Bragg angle delay device and acts to determine the time difference of arrival of electrical signals. It is useful in extracting weak radar return signals from a noisy environment. The correlation of linear FM chirp signals is illustrated in FIG. 3 of the patent. Berg et al U.S. Pat. No. 4,421,388 shows a similar frequency scanning correlator using a Bragg angle delay line. Bragg angle delay lines are also disclosed in Brienza et al U.S. Pat. No. 3,943,464 and Freyre U.S. Pat. No. 4,390,247. Freyre U.S. Pat. No. 4,443,066 discloses a dual Bragg cell system for translating or shifting the position of a coherent beam of light.